塔克拉玛干沙漠腹地大气边界层参数化方案的模拟评估

An assessment of atmospheric boundary layer schemes over the Taklimakan Desert hinterland

沙尘起沙、沉降、传输均受到沙漠地区大气边界层条件的制约。沙漠地区观测资料匮乏,限制大气边界层模拟效果的检验和评估。利用WRFV3.7.1中尺度数值模式中5种边界层参数化方案(ACM2、BL、MYJ、MYNN2.5、YSU),模拟2014年4月塔克拉玛干沙漠大气边界层特征,并与塔中80 m塔及风廓线雷达晴朗天气下的观测资料对比分析。结果表明:5种方案均能模拟出近地面气温及地表温度,边界层高度,感热、潜热、地表热通量的变化趋势,但未能模拟出边界层风速的日变化趋势,温风湿廓线能较好的反映晴日沙漠地区边界层结构的变化特征,但未模拟出风速随高度变化趋势。沙漠地区下垫面干燥,热容量低,晴天极易形成对流不稳定边界层,非局地湍流参数化方案,ACM2方案是沙漠地区大气边界层模拟较为合理的选择。

Dust emission,sedimentation and transportation are controlled by the Planetary Boundary Layer（ PBL） over the deserts. Lack of observation data in desert areas limits the examination and evaluation on PBL simulations. In this study,the performances of five PBL parameterizations of ACM2,BL,MYJ,MYNN2. 5 and YSU in the mesoscale numerical model WRF（ Weather Research and Forecast 3. 7. 1） were assessed by simulating the PBL in the Taklimakan Desert in April 2014,and compared with the observations of a 80 m tower and wind profile radar under sunny weather at Tazhong. The comparison results revealed that five PBL schemes could reasonably capture the diurnal variations of near-surface air temperature,surface temperature,boundary layer height,sensible heat,latent heat and surface heat flux,except for wind speed. Regarding the vertical PBL structures,all the simulated temperature,wind and moisture profiles can be well reproduced the boundary layer structures only with the underestimated simulations of wind speed during the daytime. The dry desert＇s thermal heat capacity is too low to easily form convective unstable boundary layer in sunny days. The combination of local and non-local ACM2 scheme could be a more appropriable PBL scheme for simulating the PBL in the desert area.